Different Radio Access Technologies (RATs), such as GERAN, UTRAN, Long Term Evolution (LTE), 1xRTT, WiMAX, and WiFi employ corresponding core networks. Mobile operators typically need to support multiple RATs for legacy wireless technologies, or due to mergers of different operators with different RAT deployments. Operators can achieve large capital and operation cost (CAPEX and OPEX) savings by deploying base station equipment supporting multiple RATs (referred to as single radio access network (RAN) solution). However, operators still need to deploy separate core networks to support the different RATs. In case of multi-RAT deployment, interoperability between different RATs needs to be guaranteed, which adds additional complexity and equipment to be deployed and maintained, and further needs new inter-working interfaces to be validated. There is a need for an improved multi-RAT architecture that enables operators to unify and simplify their core network deployments, e.g., to save cost, support legacy technologies, and further integrate new technologies.